A new Illinois law requires whooping cough vaccinations for students entering 6th and 9th grades this school year. The law requires those students to show proof they received the Tdap vaccine. Tdap is a booster shot against tetanus, diphtheria and pertussis, commonly known as whooping cough. Illinois has seen about 1,200 cases of whooping cough this year, compared to 468 cases reported as of August 1st last year.